Geophysical prospecting by application of electromagnetic surveys where a primary electromagnetic field is generated to induce a secondary electromagnetic field in an underground formation has become widespread. During the last decades, survey systems for performing such prospecting have become airborne. An airborne electromagnetic system may comprise a tow assembly connected to an aircraft, typically a helicopter, and further comprising a transmitter system for generating the primary electromagnetic field that induces the secondary electromagnetic field in the underground formation. The tow assembly tows a frame that supports the transmitter system and/or a receiving system. In other embodiments, the airborne electromagnetic system may be configured on an airplane.
Such systems are known from patent applications WO2004/046761 and WO2009/105873. Electromagnetic survey systems for geophysical prospecting are disclosed in CA2514609C and CA2776708C.
Generally larger primary electromagnetic fields have demanded larger frames and larger aircrafts. The larger frames covering hundreds of square meters require use of different materials and constructions. Besides larger frames also more complicated tow arrangements are provided to compensate for undesired effect such as changes in shape or changes in orientation during operation.
Larger and more complicated tow arrangements have shown to be difficult to handle during flight.
A one solution may be to use an “active” i.e. a propelled aircraft as a “frame” to support the transmitter, but such solution will introduce further complications.
It is an objective to overcome limitations of the prior art.